Why does `read` fail saying "read error: 0: Resource temporarily unavailable"?
script
#!/bin/bash --
# record from microphone
rec --channels 1 /tmp/rec.sox trim 0.9 band 4k noiseprof /tmp/noiseprof &&
# convert to mp3
sox /tmp/rec.sox --compression 0.01 /tmp/rec.mp3 trim 0 -0.1 &&
# play recording to test for noise
play /tmp/rec.mp3 &&
printf "nRemove noise? "
read reply
# If there's noise, remove it
if [[ $reply == "y" ]]; then
sox /tmp/rec.sox --compression 0.01 /tmp/rec.mp3 trim 0 -0.1 noisered /tmp/noiseprof 0.1
play /tmp/rec.mp3
fi
Errors with: read error: 0: Resource temporarily unavailable
But, the script works if I use the -e flag on read to enable readline
What happens is that one of your SoX programs (sox, play, rec) has changed how stdin is behaving, making it non-blocking. Typically, something is calling fcntl(0, F_SETFL, O_NONBLOCK).
When a call to the read() system call is made on a non-blocking file descriptor, the call does not wait: either there is already something to read in the kernel buffer and it is returned, or read() fails and errno is set to EAGAIN.
When Bash meets this EAGAIN error while reading from stdin with the read command, it displays the "Resource temporarily unavailable" message you have met.
Try adding <&- at the end of each of your SoX commands; this will close stdin for them and they won’t be able to alter how it is working.